PROJECT SUMMARY/ABSTRACT Alzheimer's disease and related dementias are believed to begin and progress due to a combination of genetic, lifestyle, and environmental factors. Recent studies suggest that hearing loss is associated with more rapid senescent cognitive decline and there is some evidence that partially restoring hearing with cochlear implant auditory prostheses can reduce these risks, but the specific mechanisms underlying these effects are not well understood. The basic hypothesis to be tested in this supplement to our parent grant is that the quality of the input received by cochlear-implant user will affect the extent of cognitive decline in older adults. Work currently in progress on the parent grant has demonstrated that the health of the auditory neurons which are stimulated by the cochlear implant affects the quality of information received by the listener, including their ability to recognize speech signals in quiet and in noisy environments. The parent grant initially defined auditory neural health in terms of the number of surviving spiral ganglion neurons per unit area of Rosenthal's canal (SGN density). The definition is now being expanded to include measures that reflect the integrity of neurons in the central auditory pathway. The premise of the Supplement is that across-subject differences in cognitive impairment in aging adult cochlear implant users are due in part to across-subject differences in auditory neural health. Two specific aims are proposed. Aim 1 will assess across subject differences in cognitive function in aging cochlear implant users using cognitive tests specifically adapted for people with hearing loss and compare the results to age, gender and race matched adults with relatively normal hearing and with acoustic-hearing-aid users using the same cognitive tests. Aim 2 will use electrophysiological measures of neural health to determine the extent to which peripheral and central auditory neural health are important for maintenance of cognitive health. The studies conducted under the supplement will help guide procedures for preserving auditory neural health that are being developed and tested in the parent grant and elsewhere and that promise to improve quality of life for thousands of cochlear implant users.